Biodegradable Absorbents and Methods of Preparation

ABSTRACT

A biodegradable microfiber absorbent comprises a substantially homogeneous mixture of at least one hydrophilic polymer and at least one biodegradable polymer. The absorbent can be prepared by an electro hydrodynamic spinning of a substantially homogeneous polymer mixture. Medical dressings for burns and wounds, cavity dressings, drug delivery patches, face masks, implants, drug carriers that comprises at least one microfiber electrospun from a polymer mixture are provided. The dressings can have variable water vapor penetration characteristics and variable biodegradation times.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of, and claimspriority to, copending U.S. patent application Ser. No. 11/986,751,entitled “Biodegradable absorbents and methods of preparation,” filedNov. 26, 2007, which is a continuation application of copending U.S.patent application, entitled “Biodegradable Absorbents and Methods ofPreparation,” Ser. No. 10/267,823, filed on Oct. 19, 2002, now U.S. Pat.No. 7,309,498, which claims priority to U.S. provisional patentapplication Ser. No. 60/328,454, filed on Oct. 10, 2001. The disclosuresof these copending applications are hereby incorporated by referenceherein. The present application claims priority of U.S. provisionalpatent application No. 60/328,454 filed on Oct. 10, 2001, incorporatedherein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to the field of biodegradable hydrophilicnonwoven absorbents and more particularly to microfiber biodegradableabsorbents prepared by the electrohydrodynamic method from blends ofsynthetic biodegradable polyesters and poly (N-vinyl) lactams which canbe used for a variety of applications including wounds and burnsdressings, drug carriers and for cosmetic applications.

It has been known to use poly (N-vinyl) pyrrolidone (PVP) complexes withpolyurethanes to yield hydrophilic materials, which can be used as wounddressings or in cosmetic preparations. For example, U.S. Pat. No.5,156,601 discloses a dressing, which includes a tacky gel ofpolyurethane and a poly (N-vinyl) lactam such as PVP. U.S. Pat. No.5,420,197 describes hydrophilic gels formed by poly (N-vinyl) lactams,such as PVP, and chitosan. U.S. Pat. No. 6,121,375 disclose hydrophilicgel-like materials of PVP and polyaldehyde. Other references of generalbackground interest include U.S. Pat. No. 5,206,322. All these materialsare gel-like and non-biodegradable.

Although some of these hydrophilic materials can be used for wounddressings and other surgical and cosmetic applications, many hydrophilicmaterials known in the arts are hydrophilic gels that arenon-biodegradable, and most of them are reversible.

It has also been known to make nonwoven fibrous-porous material on thebase of a blend of poly (N-vinyl) pyrrolidone (PVP) and cellulosediacetate in component weight ratio of 1:(4-10) with high porosity andhigh moisture absorption prepared “in electrostatic field by continuoussupply of an electrically charged polymeric solution through a nozzle”(Pat. RU No. 2111300). But this material is nonbiodegradable.

There is also known, Pat. RU No. 2031661, a microfibrous wound-healingremedy used for first and outdoors aid, prepared by theelectrohydrodynamic method. The remedy comprises a composition ofpoly-d.l-lactide, poly (N-vinyl) pyrrolidone and a powdered sorptivematerial like polysaccharides networks, polyacrylates, cellulose estersor polyvinyl alcohol derivatives. The material could absorb 5-8 g/gwater or blood; exhibited haemostatic abilities within 40 seconds andmoderate wound healing effects. But introduction of nondegradable orslow degradable components such as polyvinyl alcohol derivatives intothis material significantly decreased its biodegradation ability andlimited its use for external application.

There is also known, Pat. RU No. 2120306, a totally biodegradable twolayer dressing for wounds and burns consisting of a baking thin filmlayer (25-30 mkm) prepared from copoly (lactide-caprolactone) or copoly(lactide-glycolide) with a lactide/caprolactone or lactide/glycolideratio of at most 50% w and a wound facing microfiber absorbent layercomprising a polylactide and poly (N-vinyl) pyrrolidone blend with aratio of polylactide/poly (N-vinyl) pyrrolidone from 90/10 to 70/30 w/w.The microfiber absorbent layer is deposited on the film by theelectrohydrodynamic method. The facing microfiber layer may also containantiseptic, analgesic drugs and proteolysis ferments. The dressingsdescribed can absorb water and any biological liquids, including blood,at most 12 g/g and biodegrade within 12-36 days. However the vaporpenetration of such dressings is at most 3.1 mg/cm² hour which precludestheir use as dressings for wounds and burns that exhibit intensive“breathing”, for example, large external fresh burns, bleeding wounds ordifferent kinds of external injuries. Furthermore these dressings havepoorly controllable time of degradation, which limits their applicationin the treatment of wounds and/or burns, and especially in the treatmentof internal wounds. Better control over the degradation time isdesirable.

There is also known a microfiber biodegradable polylactide web preparedby the electrospinning method from a polymer solution. The polymerconcentration is 4-6% w. The voltage is 33-60 kV; the average fiberdiameter is about 1 μm (See the article in Proceeding of the ACS, PMSE,p. 115, Mar. 26-30, 2000). But there is no evidence of any hydrophilicor bioactive properties of such a web. According to the article asolution of polylactide in dichloromethane was placed in a syringe. Thesyringe was positioned with its needle pointing down, The piston of thesyringe was moved down with a controlled velocity by a motor. Thenegative pole was set at the metal capillary of the syringe and thepositive pole on the substrate bearing. Paper was used as a substrate.

SUMMARY OF THE INVENTION

Some embodiments of the invention provide dressings, implants,dermatological compatible compositions and drug carrier compositionswhich include totally biodegradable non-gel materials having water,blood and other biological liquids absorption ability and possessingbiological active properties like haemostatic and wound healingacceleration abilities, which are irreversible, retain their contour andshape when wet, and do not exhibit any swelling.

Some embodiments provide totally biodegradable microfiber absorbents onthe base of blends of synthetic biodegradable polyesters and poly(N-vinyl) lactams. These materials can be used in a variety of productssuch as cavity dressings, drug delivery patches, face masks, implants,drug carriers, wound and burn dressings with predictable biodegradationtimes and controlled absorption of biological liquids including blood,and with variable vapor penetration and controlled drug release forwounds and burns.

Some embodiments provide a method of the totally biodegradablemicrofiber absorbent preparation.

Some embodiments of the invention provide totally biodegradablemicrofiber absorbents which can be used for or incorporated intodressing compositions, dermatologicaly compatible compositions, woundpacking, wound dressings, burn dressings, living cells likekeratinocytes and/or fibroblasts transplants, drug delivery dressings,cosmetic masks, cosmetic wrap dressings, drug carrier compositions. Theabsorbents may incorporate (e.g. be soaked in) protein containing drug(e.g. insulin) and other drugs. The absorbents of the invention includea blend of synthetic biodegradable polyester and a polymer selected froma group of poly (N-vinyl)-lactams, preferably poly(N-vinyl)-pyrrolidone.

The synthetic biodegradable polyesters useful in preparing theabsorbents of the invention include, but are not limited to,homopolymers of L (−), D (+), d, l-lactide, glycolide, caprolactone,p-dioxanon and/or mixtures thereof, copolymers of L (−), D (+), d,l-lactide and glycolide, or caprolactone, or p-dioxanon, orpolyoxyethylene glycols, and/or mixtures thereof, or copolymers ofglycolide and caprolactone, or p-dioxanon. and/or mixture thereof.

The poly (N-vinyl) lactams useful in preparing the absorbents of theinvention include, but are not limited to, homopolymers, copolymers ofN-vinyl lactams such as N-vinylpyrrolidone, N-vinylbutyrolactam,N-vinylcaprolactam, and the like, as well as the foregoing prepared withminor amounts, for example, up to about 20 weight percent, of one ormore of other vinyl monomers that are capable to copolymerize with theN-vinyl lactams like acrylic monomers or others. Of the poly (N-vinyl)lactam homopolymers, the poly (N-vinyl) pyrrolidone (PVP) homopolymersare preferred. A variety of poly (N-vinyl) pyrrolidones are commerciallyavailable.

The absorbent is prepared by the electrohydrodynamic processing of ablend (a melt or a solution) of poly (N-vinyl) lactam and biodegradablepolyester. In one embodiment, the blend is a solution at apolyester/poly (N-vinyl) lactam ratio from about 99/1 to about 1/99 w/w,preferably from about 98/2 to about 50/50 w/w.

The present invention provides totally biodegradable absorbents whichare capable of absorbing at least 20 w/w in water or blood withoutswelling, are irreversible and mechanically strong, have predictablebiodegradation times, are capable of controlled medication delivery tothe body, have a variable water vapor penetration. The materials of thepresent invention have the unexpected properties such as properhaemostatic properties, enhancing the healing of wounds, especiallychronic wounds (e.g., diabetic wounds), ulcers, and proper antisepticsabilities. The dressing compositions of the present invention have theadvantage of self-adhesion to the wet skin with easy peelability.

Totally biodegradable absorbents may include at least one additionalingredient, which may be releasable from the absorbent. Preferably, thereleasable ingredients are bioeffecting or body-treating substancesincluding various low molecular weight or polymeric drugs for internalor external delivery to the body exactly where desired. Such absorbentsmay also be used as a transplantable solid support or scaffold forliving cells, such as keratinocytes or fibroblasts, growing and appliedas a living cell transplant for burns and wounds.

The totally biodegradable hydrophilic nonwoven microfiber absorbents canbe prepared by the electrohydrodynamic spinning from a polymer blendsolution using 20-120 kV at a gap distance 15-40 cm, preferably 20-40kV. The initial solution contains a blend of a biodegradable polymer anda poly (N-vinyl) lactam and may also contain different medications forimmobilization of the material. It was unexpectedly discovered that bythis method the material of the invention could be prepared.

Other benefits will be identified in the following description. Thedescription is not in any way intended to limit the scope of the presentinvention, but rather only to provide a working example of the preferredembodiments. The scope of the present invention will be pointed out inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a basic part of anelectrohydrodynamic spinning apparatus, which was used to prepare abiodegradable absorbent in one embodiment. The device contains housing1, container 2 for a polymer blend solution, power source 3 having onepole connected to a metal capillary electrode 10. The other pole isgrounded. Compressor 4 provides compressed air into container 2. Thecompressed air forces the solution out of container 2 and intoconnecting tube 11, which conducts the solution into capillary electrode10. The solution emerges from the electrode 10 as a jet flying towardsthe rotating drum 5. The electrostatic field generated by source 3 inthe area between electrode 10 and drum 5 pulls out the solution streaminto a thin thread. The solvent evaporates, and the thread becomes asolid fiber. These fibers are deposited on the surface of drum 5. Drum 5can be replace with a stationary (non-moving) substrate.

FIG. 2 is a schematic representation of a basic part of modifiedelectrohydrodynamic spinning apparatus, which was used to immobilizationfor “dry” fine powder drugs including insoluble drugs into abiodegradable absorbent. The device as shown in FIG. 1 is modified byaddition of a container 12 for a dry drug powder and of amicrocompressor 13. Compressor 13 provides compressed air into container12. The compressed air forces the powder out of container 12 and intoconnecting tube 14, which conducts the powder into a ring channel 15surrounding a capillary electrode 10. The powder is sprayed towards thegrounded surface of the rotating drum 5 and deposited simultaneouslywith the polymer microfibers or on the surface of a previously preparedmicrofiber mat.

DETAILED DESCRIPTION

Some embodiments of the invention provide a totally biodegradablehydrophilic nonwoven microfiber absorbents, impermeable to microbes,with variable degradation times and controlled vapor penetration for usein dressing, dressing compositions, drug carrier compositions, woundpacking, wound dressings, burn dressings, including first aid dressings,drug delivery dressings, cosmetic mask dressings, cosmetic wrapdressings, cavity dressings for both internal and external applications.Cosmetic applications include skin rejuvenation and wrinkle removal. Theabsorbent of the invention includes a two-component blend. One componentis a synthetic biodegradable polyester with different times ofbiodegradation selected from a group including, but not limited to,homopolymers or copolymers of L (−), D (+), d, l-lactide with glycolide,or caprolactone, or p-dioxanon, and/or mixtures thereof, or homopolymersor copolymers of caprolactone with L (−), or D (+), or d, l-lactide, orglycolide, or p-dioxanon and/or mixtures thereof, and copolymers of L(−), or D (+), or d, l-lactide, or caprolactone, or p-dioxanon withpolyoxyethylene glycols (PEG) and/or mixtures thereof, or homopolymersor copolymers of p-dioxanon. The other component is a poly (N-vinyl)lactam selected from a group including, but not limited to,homopolymers, copolymers of N-vinyl lactams such as N-vinylpyrrolidone,N-vinylbutyrolactam, N-vinylcaprolactam, and the like, as well as theforegoing prepared with minor amounts, for example, up to about 15-20weight percent, of one or more of other vinyl monomers copolymerizablewith the N-vinyl lactams such as acrylic acid, acryl amides orhydroxyalkylacrylates. Of the poly (N-vinyl) lactam homopolymers, thepoly (N-vinyl) pyrrolidone (PVP) homopolymers are preferred. A varietyof poly (N-vinyl) pyrrolidones are commercially available.

To prepare a material with controlled biodegradation times, the ratio ofpolyester/poly (N-vinyl) lactam is used in the range from about 99/1 toabout 1/99, preferably from about 98/2 to about 50/50 w/w forpolylactide, or co (poly-lactide-glycolide) with a lactide/glycolideratio from about 99/1 to about 50/50. Preferably, the poly (N-vinyl)pyrrolidone is used. Preferably, the molecular weights of the twocomponents are in the range from 3×104 to 50×104 Dalton for polyesterand from 0.5×104 to 4×104 Dalton for poly (N-vinyl) pyrrolidone. Thebiodegradable polyester component may contain caprolactone homopolymersand/or caprolactone copolymers with lactide (or glycolide) with acaprolactone/lactide (or glycolide) ratio from about 1/90 to about 99/1w/w and with the molecular weights at least 15×10⁴ Dalton for thepolyester component and the polyester/poly (N-vinyl) pyrrolidone ratiofrom about 90/10 to about 50/50 w/w. The biodegradable polyestercomponent may contain copolymers of glycolide (or lactide) andp-dioxanon with a glycolide (or lactide)/p-dioxanon ratio from about50/50 to about 1/99 w/w.

For biodegradation time control, a low molecular weight polylactide orits copolymers with glycolide may be included into the blend in theamount of at least 5-10% w. The lactide/glycolide ratio is preferably50/50 w/w. The molecular weights of these compounds are at least from2×103 to 10×103 Dalton. Various low molecular weight or polymeric linearor branched alcohols such as mannitol, sorbitol, etc. or polyoxyethyleneglycols (PEG) of different molecular weights, respectively, may beincluded into the blend in the amount of at least 5-10% w.

The totally biodegradable, hydrophilic unwoven absorbent consists ofmicrofibers at most 0.1-5 μm is irreversible with non-leachable poly(N-vinyl) lactam. The material is capable of unswelling absorption atleast 20 w/w in water or blood and/or other biological liquids with highabsorption rates without changing the contour or shape of the device.The material is capable of delivering medicaments externally orinternally to the body exactly where desired. The material of thepresent invention has by itself unexpected properties such as ahaemostatic property and antiseptics property. The material enhances thehealing of wounds, especially chronic wounds (e.g., diabetic wounds) andulcers and may be applied without any additional medications. Thematerial and its degradation products are biocompatible and don't induceany tissues immune response. The products based on the materials of thepresent invention have a good mechanical strength and preserve theirshape under wet conditions. They can be sterilized by X-ray radiation.Other advantages obtained in some embodiments include softness andcompliance with skin surfaces, and self-adhesion to the wet skin butwith easy peelability and a variable “breathability”.

To obtain a totally biodegradable, hydrophilic unwoven absorbent, theelectrohydrodynamic method for solution spinning can be applied. Themethod involves spraying the solution of a polymer blend through acapillary nozzle onto a substrate. More particularly, the methodconsists in providing a stream of compressed air or some other gasthrough a capillary nozzle, and continuously introducing into the airstream a solution of a blend of a biodegradable polyester and poly(N-vinyl) pyrrolidone or other poly (N-vinyl) lactams in a solvent (e.g.dichloromethane or mixture of ethyl acetate and a lower alcohol. Anexemplary concentration of the polymer in the solution is 1-40% w. Thevoltage between the nozzle and the substrate can be 20-120 kV,preferably 20-40 kV. The negative pole is set at the metal capillary ofthe nozzle. The substrate is grounded. The gap between the nozzle andthe substrate is 15-40 cm. Depending on the voltage, gap value andpolymer in the solution concentration, materials of a controlled densityand microfiber diameters from 0.1-5 μm can be prepared. After thecompletion of the process the microfiber unwoven material is removedfrom the substrate, cut into pieces (for example, squares) and vacuumdried. A finished product is packed and sterilized by γ-radiation byconventional techniques.

The substrate can be either a static surface or a rotating drum asdescribed in Russian patent RU 2121036 (20 Oct. 1998).

FIG. 1 shows a schematic representation of a basic part of an apparatusof electrohydrodynamic spinning which was used for biodegradableabsorbent of the invention preparation. The device contains housing 1,container 2 for polymer blend solution used for spinning, power source 3connected to metal capillary electrode by one pole with the second polesetting grounded, compressor 4 connected with the container 2. Thesolution of a blend of a biodegradable polymer and poly (N-vinyl) lactamin a solvent is providing by a stream of compressed air from compressor4 through a capillary nozzle with high voltage imposed from the source3. A polymer solution jet flowing out of the capillary nozzle in thestream of compressed air under the action of electrostatic field forcesis drawing off into at least one ultra thin fiber that is deposited on agrounded substrate surface that can be a rotating drum 5 or non-movingsubstrate. For apparatus productivity increase the device can besupplied with an additional compressed air source 13 comprising a ringchannel 15 surrounding a capillary electrode 10 (FIG. 2).

Materials with a different degree of “breathability” can be obtainedthrough: 1) selection of the microfiber thickness and packing density;2) electrohydrodynamic microfiber deposition on at least 5-10 μm thickpolymeric films of the appropriate breathability. These films can beprepared from biodegradable polymers and copolymers like polylactide, orpoly (lactide-co-glycolide) with a lactide/glycolide ratio from about1/99 to about 99/1, or poly (lactide-co-caprolactone) with alactide/caprolactone ratio from about 1/99 to about 99/1,polycaprolactone, poly-p-dioxanon or its copolymers with glycolide orlactide with a p-dioxanon/lactide or glycolide ratio from about 1/99 toabout 99/1. These biodegradable films, which serve as backing films insuch dressings, may be prepared by any conventional methods of polymerprocessing from either a polymer melt or a polymer solution. A backingfilm with variable vapor permeability (i.e. breathability) can also beprepared from a mixture of biodegradable polyesters listed above andother biocompatible polymers of various molecular weights likepolyoxyethylene glycols in the amount of at least 15% w. The backingfilm may also improve the mechanical properties of the dressings.

The “breathability” can also be increased by increasing the gap betweenthe nozzle and the substrate if the electrohydrodynamic method is used.The “breathability” is believed to decrease if a higher voltage is usedbetween the nozzle and the substrate. These techniques (gap size andvoltage) can be used with or without the backing film. Moreparticularly, in some embodiments, no backing film is present. Theabsorbent material is formed by the electrohydrodynamic method on asubstrate as described above. The substrate can be a rotating drum.After this electrohydrodynamic deposition, the absorbent article isremoved from the substrate. The article can be used without any backingfilm. Non-drum substrates including non-moving substrates, can be used.

The absorbent of the invention may also include at least one additionalingredient, which may be releasable from the absorbent. Preferably, thereleasable ingredients are bioeffecting or body-treating substancesincluding different low molecular weight or polymeric drugs for internalor external delivery to the body exactly where desired. Particularlypreferred as biologically-active additives are also antimicrobials suchas tetracycline, neomycin, oxytetracycline, triclosan, sodium cefazolin,silver sulfadiazine, and also salicylates such as methylsalicylate andsalicylic acid, nicotinates such as methyl nicotinate; capsaicin,benzocaine, alpha-hydroxy acids, vitamins and biostats and others, orantioncology active drugs like doxorubicin, toxol and others or insulin,or interferon, or others.

When the material is used for wound and burn healing acceleration, itmay contain living human cells like keratinocytes or fibroblastspreviously grown on the material as on the solid porous scaffold.

To provide a prolonged and controlled drug release to the surface ofinternal and/or external wounds or burns, the material may contain twoor more microfiber layers. Different layers may have differentcompositions. Each layer includes the biodegradable polymer with orwithout poly (N-vinyl) lactam. Different layers may also have differentratios of biodegradable polymer/poly (N-vinyl) lactam or differentbiodegradable polymers. Different types of polymers and/or copolymersmay be used that may have different molecular weights, contain differentbiocompatible functional groups such as hydroxyl, carboxyl and/or aminogroups or contain different additives such as low or high molecularweight alcohols like sorbitol, mannitol, starch, polyoxyethyleneglycols, etc. Each layer may include at least one additional bioactiveingredient which may be releasable from the absorbent and which may beimmobilized into polymeric matrix as by the electrohydrodynamic methodas by conventional methods such as wetting of the material by drugsolution.

When the electrohydrodynamic method is used for drug immobilization intoan absorbent, the drug can be dissolved in a polymeric blend solutionand immobilized using the device shown in FIG. 1 or can be immobilizedas dry fine particles by compressed air steam using the modified deviceshown in FIG. 2.

For drug delivery systems, the material of the present invention maycontain drugs immobilized by the electrohydrodynamics or other methodsand then ground into fine particles of a size less than 10 μm. Theseparticles can be used for parenteral drug administration as a suspensionin water, or for oral delivery after tableting the particles prepared byconventional compression methods. Tablets for oral drug delivery mayalso be prepared by conventional methods of tablet compression of thenon-ground material with immobilized drugs. For drug carrier usage, thematerial may be prepared for example from the blend of polylactide andpoly (N-vinyl) pyrrolidone, and polylactide molecular weights are atleast 5×104 Dalton. The following examples are intended to illustratebut not limit the invention. The claim will serve to define theinvention.

In the following examples the preparation of biodegradable absorbents isdescribed, which absorbents can be used as wound and burn dressings,drug carriers and for cosmetic applications. These examples should notbe viewed as limiting the scope of the invention. The claims will serveto define the invention.

Example 1 A Biodegradable Absorbent Utilizing Microfibres ContainingPoly (Lactide-Co-Glycolide and/or Poly-N-Vinyl) Pyrrolidone withVariable “Breathing” Capabilities Materials:

Poly (d.l-lactide-co-glycolide) with a lactide/glycolide ratio 70/30 w/wand with an average molecular weight of 150000 Dal and Poly-d.l-lactidewith an average molecular weight of 230000 Dal was synthesized byconventional ring-opening polymerization from d.l-lactide and glycolidethat were purchased from Russian National Institute of Monomers (Tula,Russia). Poly-(N-vinyl) pyrrolidone with an average molecular weight of30000 Dal was purchased from a Russian enterprise.

Methods. 1. Solution Preparation.

Poly (d.l-lactide-co-glycolide) (PLGA) was dissolved in ethyl acetate tomake a 20% (w/w) solution with solution viscosity 1-2 poise (Solution A)or a 10% (w/w) solution with solution viscosity 0.5 poise (Solution B).Poly-(N-vinyl) pyrrolidone (PVP) was dissolved in ethanol making a 20%(w/w) solution and mixed with the PLGA solution in ethyl acetate atPVP/PLGA ratio of 20/80 (w/w) that was used for the electrohydrodynamicspinning.

2. Microfiber Material Preparation.

The PLGA/PVP solution was filtered to remove mechanical and gel-likeimpurities and was placed into a container 2 (FIG. 1) and spun intowound dressing materials in the form of microfiber mats, which werecollected on the surface of a rotating drum 5 or on a film positioned onthe surface of a rotating drum 5 that is used as a substrate. After thecompletion of the process, the microfiber unwoven material was cut intosquares and vacuum dried to remove the solvent residue. The finishedproduct was packed into a polyethylene laminated aluminum foil andsterilized by 2.5 Mrad γ-radiation using a conventional procedure.

3. Measurements of Microfiber Material Properties.

To measure the degree of absorbency, 2 cm² strips (0.5×4 cm) of themicrofiber mat were cut and weighed (dry weight or DW), The end of thenarrow side (0.5 cm side) of the strip was immersed in water or bloodand soaked for 10-15 min. The liquid was drained and the strip wasweighed (wet weight or WW). The content of water or blood absorbed bythe material calculated using the equation:

Water/blood absorbed content=(WW−DW)/DW,g/g

Data on biodegradation times and haemostatic abilities of the materialwere obtained from in vivo experiments.

Sample 1.

Solution A: (PVP/PLGA in ethyl acetate, 20% PLGA) was spun by theelectrohydrodynamic method with 30 kV at 25 cm gap distance L (FIG. 1)for 1 hour. The microfiber thickness was around 1.5-2 μm with a surfacedensity (a coating level) ˜5 mg/cm².

Sample 2.

Solution B: (PVP/PLGA in ethyl acetate, 10% PLGA) was spun by theelectrohydrodynamic method with 30 kV at 25 cm gap distance L (FIG. 1)for 1 hour. The microfiber thickness was around 0.5-1 μm with a surfacedensity (a coating level) ˜2.5 mg/cm².

Sample 3.

Solution A: (PVP/PLGA in ethyl acetate, 20% PLGA) was spun by theelectrohydrodynamic method with 40 kV at 25 cm gap distance L (FIG. 1)for 1 hour. The microfiber thickness was around 1-1.5 μm with a surfacedensity (a coating level) ˜5 mg/cm².

Sample 4.

Solution A: (PVP/PLGA in ethyl acetate, 20% PLGA) was spun theelectrohydrodynamic method with 30 kV at 40 cm gap distance L (FIG. 1)for 1 hour. The microfiber thickness was around 1.5-2 μm with amicrofiber surface density (a coating level) ˜3 mg/cm².

Sample 5.

Solution A: (PVP/PLGA in ethyl acetate, 20% PLGA) was spun by theelectrohydrodynamic method with 30 kV at 25 cm gap distance L (FIG. 1).Drum 5 was covered by a poly (d.l-lactide) film (backing film) having athickness of 8-10 μm. The film was formed from 10% w solution ofPoly-d.l-lactide in methylene chloride. The microfibers were depositedon the film. The fiber size was around 1.5-2 μm with a microfibersurface density (a coating level) ˜5 mg/cm².

Test results for the materials in Samples 1-5 are summarized in Table 1.

TABLE 1 Physical-chemical and biomedical properties of biodegradableabsorbents. Moisture vapor Water/Blood Times of Sample penetration,absorbance, biodegradation Microbial # Mg/cm² hour g/g in vivo*, dayspenetration 1 5-7 15-20/19-20 3-5 Non penetrable 2 2-3.5 10-15/14-18 3-5Non penetrable 3 5-7 12-15/16-18 3-5 Non penetrable 4 7-8 12-15/16-183-5 Non penetrable 5 2-2.7 15-20/18-20 7-8 Non penetrable *Visualobservation of in vivo degradation of equal square pieces of thematerial on the surface of fresh clean wounds formed on rat skin.

Example 2 Preparation of Fiber and/or Biodegradable Absorbent withAdditional Therapeutic Performance Sample 1.

Silver sulfadiazine was dissolved under slight heating in ethanol toform a 5% solution and then added to the PLGA/PVP solution describedabove to yield a 1% silver sulfadiazine concentration in the finalmaterial. The solution was spun by the electrohydrodynamic method with30 kV at 25 cm gap distance L (FIG. 1) for 1 hour. The microfiberthickness was around 1.5-2 μm with a surface density (a coating level)˜5 mg/cm².

Sample 2.

Silver sulfadiazine in the form of fine particles was placed intocontainer 12 (FIG. 2) and immobilized using a compressed air stream(˜0.5 atm) onto the surface of a just prepared absorbent deposited on asurface of a rotating drum using 30 kV at a gap distance 25 cm.

The invention is not limited by the embodiments described above, Forexample, in the electrohydrodynamic method, an alternating electricfield can be used. Also, solutions can be replaced by melts. Otherembodiments are within the scope of the invention as defined by theappended claims.

1. A biodegradable structure comprising an electrohydrodynamic processedmixture containing: (a) a solvent; (b) poly-(N-vinyl)pyrrolidone; and(c) a biodegradable polyester which includes a caprolactone or adioxanon of a molecular mass at least 125000 Dalton, with a componentratio of the poly-(N-vinyl)pyrrolidone to the caprolactone or diaxanonby weight being from about 2:98 to about 9:91 or from about 31:69 toabout 50:50.
 2. The biodegradable structure of claim 1, wherein saidmixture further comprises one or more low molecular weight biodegradablepolyesters with hydroxyl, carboxyl or amino-terminal groups, or one ormore polyoxyethylene glycols, or one or more low molecular weightalcohols selected from the group containing alcohols, including alcoholsof natural origin.
 3. The biodegradable structure of claim 1, furthercomprising one or more of living cells, proteins, peptides, antibioticcompounds, bacteriocidal compounds, fungicidal compounds, bacteriostaticcompounds, analgesic compounds, and trombogenic compounds.
 4. Thebiodegradable structure of claim 1, wherein the mixture furthercomprises one or more biodegradable polyesters with hydroxyl, carboxylor amino-terminal groups, and/or one or more polyoxyethylene glycols, orone or more alcohols.
 5. The biodegradable structure of claim 1, whereinthe mixture further comprises a compound selected from the groupconsisting of polyoxyethylene glycol, salicylates, methylsalicylate,salicylic acid, and nicotenates.
 6. The biodegradable structure of claim1, wherein the mixture further comprises an antimicrobial substance. 7.The biodegradable structure of claim 1, wherein the mixture furthercomprises a compound selected from the group consisting of tetracycline,neomycin, oxytetracycline, triclosan, sodium cefazolin, doxorubicin,toxol, insulin, and interferon.
 8. The biodegradable structure of claim1, further comprising one or more alpha hydroxy acids.
 10. Thebiodegradable structure of claim 1, wherein the mixture furthercomprises at least one copolymer that includes a polyether or apolyoxyethylene glycol and a polymer of a lactides, a dioxanon, acaprolactone or a glycolide.
 11. A method for preparing a biodegradablemicrofiber absorbent, the method comprising electrohydrodynamicprocessing of a mixture containing: (a) a solvent; (b)poly-(N-vinyl)pyrrolidone; and (c) a biodegradable polyester whichincludes a caprolactone or a dioxanon of a molecular mass at least125000 Dalton, with a component ratio of the poly-(N-vinyl)pyrrolidoneto the caprolactone or diaxanon by weight being from about 2:98 to about9:91 or from about 31:69 to about 50:50.
 12. The method of claim 11,wherein said mixture further comprises one or more low molecular weightbiodegradable polyesters with hydroxyl, carboxyl or amino-terminalgroups, or one or more polyoxyethylene glycols, or one or more lowmolecular weight alcohols selected from the group containing alcohols,including alcohols of natural origin.
 13. The method of claim 11,further comprising incorporating into the absorbent at least onetherapeutic performance enhancing additive comprising one or more ofliving cells, proteins, peptides, antibiotic compounds, bacteriocidalcompounds, fungicidal compounds, bacteriostatic compounds, analgesiccompounds, and trombogenic compounds.
 14. The method of claim 11,wherein the electrohydrodynamic processing comprises emitting a flow ofsaid mixture into an area in which said mixture flies in an electricalfield towards a substrate; and the method further comprises emitting aflow of dry particles into said area and the dry particles beingdeposited over said substrate.
 15. The method of claim 14, wherein theflow of dry particles and the flow of said mixture are emitted into saidarea in overlapping periods of time.
 16. The method of claim 11, whereinthe mixture further comprises at least one therapeuticperformance-enhancing additive.
 17. The method of claim 11, wherein themixture has an intrinsic viscosity from about 0.1 to about 10 poise. 18.The method of claim 11, wherein the mixture further comprises one ormore biodegradable polyesters with hydroxyl, carboxyl or amino-terminalgroups, and/or one or more polyoxyethylene glycols, or one or morealcohols.
 19. The method of claim 11, wherein the mixture furthercomprises a compound selected from the group consisting ofpolyoxyethylene glycol, salicylates, methylsalicylate, salicylic acid,and nicotenates.
 20. The method of claim 11, wherein the mixture furthercomprises an antimicrobial substance.
 21. The method of claim 11,wherein the mixture further comprises a compound selected from the groupconsisting of tetracycline, neomycin, oxytetracycline, triclosan, sodiumcefazolin, doxorubicin, toxol, insulin, and interferon.
 22. The methodof claim 11, further comprising including into the mixture one or morealpha hydroxy acids.
 23. The method of claim 11, wherein the mixturefurther comprises at least one copolymer that includes a polyether or apolyoxyethylene glycol and a polymer of a lactides, a dioxanon, acaprolactone or a glycolide.
 24. A method for preparing a biodegradablemicrofiber absorbent, the method comprising electrohydrodynamic spinningof a substantially homogeneous mixture comprising at least onehydrophilic polymer and at least one biodegradable polymer, theelectrohydrodynamic spinning being performed at a voltage from about 20to about 30 kV or from about 65 to about 90 kV.